U.S. patent application number 14/897113 was filed with the patent office on 2016-05-19 for steel part and method for manufacturing the same.
The applicant listed for this patent is HITACHI, LTD.. Invention is credited to Kousuke KUWABARA, Minseok PARK.
Application Number | 20160138151 14/897113 |
Document ID | / |
Family ID | 52021759 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160138151 |
Kind Code |
A1 |
KUWABARA; Kousuke ; et
al. |
May 19, 2016 |
Steel Part and Method for Manufacturing the Same
Abstract
A plurality of layers are laminated on at least part of the
member under treatment made of steel, the plurality of layers
having carbon concentrations higher than that of the member under
treatment and 1.0 wt. % or less, the carbon concentration of an
outermost layer of the plurality of layers being the highest. A
method for manufacturing a steel part, including spraying powder
containing carbon on at least part of an member under treatment
made of steel so as to form a first layer having a carbon
concentration higher than that of the member under treatment and
spraying powder containing carbon on at least part of the first
layer so as to form a second layer having a carbon concentration
higher than that of the first layer. Carbon concentrations of a
plurality of layers including the first layer and the second layer
are 1.0 wt. % or less.
Inventors: |
KUWABARA; Kousuke; (Tokyo,
JP) ; PARK; Minseok; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI, LTD. |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Family ID: |
52021759 |
Appl. No.: |
14/897113 |
Filed: |
June 10, 2013 |
PCT Filed: |
June 10, 2013 |
PCT NO: |
PCT/JP2013/065916 |
371 Date: |
December 9, 2015 |
Current U.S.
Class: |
148/206 ;
148/319 |
Current CPC
Class: |
C23C 28/048 20130101;
C23C 24/04 20130101; C23C 8/66 20130101; C23C 4/18 20130101; C23C
4/06 20130101 |
International
Class: |
C23C 8/66 20060101
C23C008/66; C23C 28/04 20060101 C23C028/04; C23C 4/06 20060101
C23C004/06 |
Claims
1. A steel part having a member under treatment made of steel, a
plurality of layers being laminated on at least part of the member
under treatment, the plurality of layers having carbon
concentrations higher than that of the member under treatment and
1.0 wt. % or less, the carbon concentration of an outermost layer
of the plurality of layers being the highest.
2. The steel part according to claim 1, wherein the plurality of
layers are three layers or more.
3. The steel part according to claim 1, wherein the member under
treatment has an area in which the plurality of layers are
laminated and an area in which the plurality of layers are not
laminated.
4. The steel part according to claim 1, wherein the plurality of
layers includes a first layer and a second layer laminated
successively on the member under treatment, the first layer having
an area in which the second layer is laminated and an area in which
the second layer is not laminated.
5. A method for manufacturing a steel part, comprising: spraying
powder containing carbon on at least part of an member under
treatment made of steel so as to form a first layer having a carbon
concentration higher than that of the member under treatment; and
spraying powder containing carbon on at least part of the first
layer so as to form a second layer having a carbon concentration
higher than that of the first layer, wherein carbon concentrations
of a plurality of layers including the first layer and the second
layer are 1.0 wt. % or less.
6. The method for manufacturing the steel part according to claim
5, comprising: spraying powder containing carbon on at least part
of the second layer so as to form a third layer having a carbon
concentration higher than that of the second layer.
7. The method for manufacturing the steel part according to claim
5, wherein the plurality of layers are formed while the member
under treatment is heated.
Description
TECHNICAL FIELD
[0001] The present invention relates to a steel part and a method
for manufacturing the same.
BACKGROUND ART
[0002] Since machine parts such as drive parts, gears, and bearings
are always exposed. to heavy loads, they need to have high
mechanical strength such as hardness and fatigue resistance. These
machine parts are made from steels used for machine structures such
as carbon steel, chromium. steel, chromium molybdenum steel, and
nickel chromium-molybdenum steel.
[0003] The steels used for machine structures may need two opposite
properties for an outer portion and an inner par Lion, that is, a
surface of the steels needs high fatigue resistance and the
material itself needs high fracture resistance to secure shock
resistance of the part. The material may have a base material
having a comparatively low carbon concentration and a high fracture
resistance, for example, a low alloy steel (such as SCM415 defined
in JIS-G4104). The surface of the material is often solid-soluted
with carbon so as to increase the carbon concentration, and
carburizing treatment and carbonitriding treatment are often
performed to improve hardness and fatigue resistance.
[0004] However, when carbon is simply dispersed on the surface of
the material, a surface hard layer has a gradient in carbon
concentration distribution. Thus, it is difficult to form a thick
composition having a desired carbon concentration. When the surface
hard layer is thickened, the surface is excessively carburized
(excessive carburization). As a result, the surface hard layer
embrittles. For example, PTL 1 discloses a method for forming a
hard film of high carbon steel or a high-carbon low-alloy steel on
a surface of a base material and thermally diffuse-bonding the base
material and the hard film so as to secure desired strength.
CITATION LIST
Patent Literature
[0005] PTL 1: JP 11-222663 A.
SUMMARY OF INVENTION
Technical Problem
[0006] However, according to the method disclosed in PTL 1, since
there is a large difference between the carbon concentration of the
base material as a member under treatment and that of the coating
film of the high carbon steel, the member under treatment and the
surface hard layer easily peel off between the base material and
the coating film, which is a problem of such a method.
[0007] An object of the present invention is to prevent the member
under treatment and the surface hard layer from peeling off.
Solution to Problem
[0008] To accomplish the foregoing object, configurations described
for example in the claims are used.
Advantageous Effects of Invention
[0009] According to the present invention, the member under
treatment and the surface hard layer can be prevented from peeling
off.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is an example of a block diagram of a steel part.
[0011] FIG. 2 is an example of a block diagram of the steel
part.
[0012] FIG. 3 is an example of a process drawing showing a process
for forming a first layer and a second layer on a member under
treatment.
[0013] FIG. 4 is an example of a schematic diagram showing a steel
part according to a second example.
[0014] FIG. 5 is an example of a schematic diagram showing a cross
section of the steel part according to the second example.
[0015] FIG. 6 is an example of a process drawing showing a process
for forming a steel part according to the second example.
DESCRIPTION OF EMBODIMENTS
[0016] A steel part according to the present invention includes a
plurality of layers having high carbon concentrations than that of
a member under treatment (high carbon steel layers) formed on the
surface of the member under treatment (steel, part). The carbon
concentrations of the high carbon steel layers are 1.0 wt. % or
less. The outermost layer has the highest carbon concentration.
[0017] FIG. 1 shows an embodiment of the present invention. A first
layer 102 and a second layer 103 are successively laminated on at
least part of a member under treatment 101 so as to form a steel
part 100. The first layer 102 and the second layer 103 are high
carbon steel layers having carbon concentrations of 1.0 wt. % or
less. The carbon concentrations of the first layer 102 and the
second layer 103 are higher than that of the member under
treatment. The carbon concentration of the second layer is higher
than that of the first layer.
[0018] FIG. 2 shows another embodiment. According to the present
embodiment, a third layer 104 is laminated on the second layer of
the steel part shown in FIG. 1. The carbon concentration of the
third layer 104 is higher than that of the second laver. The carbon
concentration of the third layer 104 is 1.0 wt. % or less.
[0019] Examples of the member under treatment on which a surface
treatment is performed includes low carbon steel or low carbon
alloy steel. The materials having high fracture resistance such as
chromium steel, chromium molybdenum steel, chromium molybdenum
nickel steel, chromium manganese steel, and chromium nickel, steel
(stainless steel) are exemplified, and alloy compositions thereof
are defined in domestic and foreign standards such as JIS and
ASTM.
[0020] The plurality of high carbon steel layers coating the member
under treatment is required to have carbon concentrations that are
higher than that of the member under treatment and 1.0 wt. % or
less. Since the carbon concentrations of these layers are higher
than that of the member under treatment, these layers have higher
fatigue resistances. In addition, when the carbon concentrations of
these layers are 1.0 wt. % or less, mesh-shaped cementite can be
prevented from excessively deposited on a grain boundary. Thus, the
surface can be prevented from embrittling, and as a result, these
high carbon steel layers become long fatigue-life layers. The high
carbon steel lavers have at least the first layer and the second
layer. When necessary, the high carbon steel layers also have one
or more layers formed on the first and second layers. The carbon
concentration increases from the member under treatment toward the
outermost layer.
[0021] To increase the carbon concentration of the steel part by
coating the member under treatment with the layer without
carburizing and diffusing, a plurality of layers is formed to
decrease differences of carbon concentrations between the layers,
and therefore, peeling between the member under treatment and the
high carbon steel layer and peeling, cracking and the like between
the high carbon steel, layers can be reduced. In addition, the
desired carbon concentrations and thicknesses of the layers can be
freely adjusted. When the layer is a multi-layer composed of three
or more layers, even if the difference between the carbon
concentration of the outermost layer and the carbon concentration
of the member under treatment is large, since the differences of
carbon concentrations of individual layers can be decreased,
peeling between the member under treatment and the layer and
peeling and the like between the layers can be reduced.
[0022] Although the drawing clearly separates layers, since carbon
slightly diffuses from a layer that has a high carbon concentration
to a layer that has a low carbon concentration, there is a gentle
gradient of carbon concentrations at boundaries of layers in the
film thickness direction. According to the present invention, a
portion where there is a gradient of carbon concentrations is
permitted as inter-layers (boundaries of layers).
[0023] Alloy compositions other than carbon of individual layers
are not restricted. Examples of these steel materials are high
carbon steel and high carbon alloy steel. In particular, it is
preferable that the compositions of alloy elements of the first
layer, the second layer, and at least one layer formed thereon if
necessary (hereinafter these layers are referred to as the
plurality of high carbon steel layers) are nearly the same as that
of the member under treatment, so that the high carbon steel layers
can be unified with the member under treatment and that a
conjugated compound can be prevented from locally being formed.
Alternatively, other alloy elements may be adjusted so as to
improve properties such as corrosive resistance and heat resistance
other than fatigue resistance, at the same time.
[0024] Although the plurality of high carbon steel layers may be
formed on the entire surface of the member under treatment with
equal thicknesses, the plurality of high carbon steel layers may
have a thickness distribution on the surface of the member under
treatment, and may be formed only on part of the member under
treatment. As a particular example from machine parts, each of the
layers may be formed only at a portion that needs especially high
fatigue resistance such as a contact portion with a bearing of a
shaft, tooth of a gear, a contact portion with a member of a press
roll. These partial treatments are preferable when a portion that
needs fracture resistance and a portion that needs fatigue
resistance are individually controlled. Further, each of the layers
may be formed on the surface of the member under treatment with
distribution such as a portion having no layers, a portion having
only the first layer, and a portion having both the first layer and
the second layer. Likewise, at least one layer formed on the second
layer may be formed on part of the surface of the member under
treatment.
[0025] The plurality of high carbon steel layers can be formed
according to various methods. As methods that are excellent in
forming speed and adherence to the member under treatment, a cold
spraying method, a warm spraying method, a plasma spraying method,
an arc spraying method, a flame spraying method, a building-up
welding method, an aerosol deposition method, and so forth are
known. FIG. 3 shows a process for successively forming individual
layers.
[0026] (a) A member under treatment 101 is prepared to form high
carbon steel layers.
[0027] A first layer 102 is formed on the member under treatment
101. Materials of the individual layers are prepared in the form of
powder, wires, rods, and the like, according to the individual
methods. According to the method shown in FIG. 3, powder is sprayed
to be deposited on the member under treatment. For example, using
powder having a low carbon concentration (first powder), the layer
is formed according to the foregoing method. The carbon
concentration of the first powder is higher than that of the member
under treatment and 1.0 wt. % or less. Alternatively, the first
powder may be a mixture of carbon and another powder. When the
layer is formed, the carbon concentration of the layer contained in
the entire layer may be higher than that of the member under
treatment and 1.0 wt. % or less.
[0028] (c) A second layer 102 is formed on the first layer 102. The
second layer is formed on the first layer 102 using powder (second
powder) having a higher carbon concentration than that of the first
layer. Like the first powder, the second. powder may be a mixture
of carbon and another powder. When the layer is formed, the carbon
concentration of the entire layer may be higher than that of the
first layer and 1.0 wt. % or less.
[0029] (d) As a result, a steel part 100 having two high carbon
steel layers is formed.
[0030] Even if the high carbon steel layers is a multilayer, it is
preferable that the mixing ratios of a plurality of types of
powders having different carbon concentrations are changed, because
the kinds of materials required for forming the layer. Although
film forming conditions are appropriately adjusted depending on a
method, a member under treatment, and materials of individual
layers that are used, it is preferable to form the layer at a
temperature of the member under treatment higher than the room
temperature, because the film forming efficiency is improved,
adherence of each of the layers to the member under treatment is
improved, and mutual diffusion on the interface of each of the
layers is accelerated. However, it is desirable that the film
forming temperature is adjusted depending on various conditions
such as heat resistances and oxidizing resistances of the materials
of the member under treatment and the individual layers. After
forming the layers as described above, thermal treatment such as
quenching and annealing and surface treatment such as carburizing
and nitriding can be performed.
[0031] Hereinbelow, examples will be described with reference to
the accompanying drawings.
EXAMPLE 1
[0032] In the present example, an example in which the steel part
100 is a plate will be described. FIG. 1 is a block diagram of the
steel part 100 in the present example. In the present example, the
member under treatment 101 used for the steel part 100 was a
stainless steel plate having a length of 50 mm, a width of 50 mm,
and a. thickness of 10 mm (JIS standard: SUS 304, NISSHIN STEEL
CO., LTD, 0.05 wt. %).
[0033] The first layer 102 and the second layer 103 were made from
stainless steel powder (DAP304L, DAIDO STEEL LTD). Two types of
powder, stainless steel powder A that is additive free and
stainless steel powder B that holds graphite powder of 2.0 wt. %
(SIGMA-ALDRICH CO. LLC) were mixed at predetermined weight ratios
to prepare material powders of the first layer 102 and the second
layer 103. In the present example, the material powders of the
first layer 102 were mixed so that the carbon concentration became
0.4 wt. % (stainless steel powder A: stainless steel powder B=8:2
(weight ratio) and the material powders of the second layer 103
were mixed so that the carbon concentration became 0.8 wt. %
(stainless steel powder A: stainless steel powder B=6:4 (weight
ratio), and the mixed material powders were uniformly maxed by a
V-shape rotating mixer to prepare the material powders of each of
the first layer 102 and the second layer 103. FIG. 1 is a schematic
diagram showing individual layers so that they can be easily
distinguished. Table 1 lists real thicknesses of individual films
that are formed. Theoretically, the carbon concentrations when the
powder is adjusted matches the carbon concentrations of the formed
layers. However, since carbon is lost while materials are adjusted
and layers are formed, the carbon concentrations of the layers are
slightly lower than those of the material powders.
[0034] FIG. 3 shows a process for forming the first layer and the
second layer in the present example. The first layer and the second
layer were formed by a cold spraying method under the condition
that nitrogen gas was used as carrier gas at a pressure of 4 MPa,
the temperature of the member under treatment was 400.degree. C.,
and the nozzle distance was 20 mm. When the member under treatment
is heated, since powder easily adheres to the member under
treatment, the adherence between layers further improves.
Thereafter, material powders were changed and the second layer was
formed by the cold spraying method in the same conditions.
Thereafter, the heat treatment was performed at 800.degree. C. for
30 minutes so that graphite powder held on stainless steel powder B
was solidified in each of the layers and then quenching is
performed at a speed of 100.degree. C. per second to form the steel
part 100.
COMPARATIVE EXAMPLE 1
[0035] In the configuration of Example 1, a first layer having a
carbon concentration of 0.8 wt. % was formed by the cold spraying
method, and a second layer was not formed. The other forming
conditions were the same as those of Example 1.
[0036] In Example 1, also in a Falex test conducted with a test
piece of around 1 mm thick and Vickers hardness (Hv) of 920 on the
surface of the steel part 100, the surface treatment layer having
good adherence without inter-laver peeling can be obtained.
However, in Comparative Example 1, there was a problem in adherence
due to small peeling between the member under treatment 101 and the
first layer 102.
TABLE-US-00001 TABLE 1 EXAMPLE COMPARATIVE 1 EXAMPLE 1 FIRST
THICKNESS (mm) 0.10 1.03 LAYER AVERAGE CARBON 0.36 0.75
CONCENTRATION (wt. %) VICKERS HARDNESS 710 910 (Hv) SECOND
THICKNESS (mm) 1.01 LAYER AVERAGE CARBON 0.77 CONCENTRATION (wt. %)
VICKERS HARDNESS 920 (Hv) ADHERENCE BETWEEN BASE NO CRACKING
MATERIAL AND LAYER PEELING
EXAMPLE 2
[0037] In the present example, an example in which a steel part 100
is a shaft part will be described. FIG. 4 is a schematic diagram of
the steel part 100. The steel cart 100 used a member under
treatment 101 of chrome molybdenum steel (JIS standard.: SCM 415,
DAIDO STEEL CO., LTD., 0.15 wt. %) having a diameter of 30 mm and a
length of 300 mm. A first layer 102, a second layer 103, and a
third layer 104 were formed at an end portion of the member under
treatment.
[0038] FIG. 5 is a sectional view taken along a line A-A' of FIG.
4. FIG. 5 shows a cross section to a line C-C. The first layer 102,
the second layer 103, and the third layer 104 were formed at the
end portion of the member under treatment 101. All the three layers
were formed within 100 mm from the end portion, the first layer 101
and the second layer 102 were formed at the portion between 100 mm
and 110 mm from the end portion, and only the first layer 101 was
formed at the portion between 110 mm and 120 mm from the end
portion of the member under treatment 101. FIG. 4 is a schematic
diagram showing individual layers so that they can be easily
distinguished. Table 2 lists real thicknesses of individual films
that are formed.
[0039] Each of these layers was made by mixing two types of powder,
chrome molybdenum steel powder A and chrome molybdenum steel powder
B at predetermined weight ratios. Chrome molybdenum steel powder A
is made of chrome molybdenum steel powder (SCM 415, EPSON ATMIX
CORPORATION) that has the same composition as that of the member
under treatment 101, and chrome molybdenum steel powder B is made
by increasing only the carbon concentration of the chrome
molybdenum steel powder A to 2.0 wt. %, to prepare the material
powders of these layers. In the present example, the material
powders of the first layer 102 were mixed so that the carbon
concentration became 0.4 wt .% (chrome molybdenum steel powder A:
chrome molybdenum steel powder B=86:14 (weight ratio)), the
material powders of the second layer 103 were mixed so that the
carbon concentration became 0.6 wt. % (chrome molybdenum steel
powder A: a chrome molybdenum steel powder B=76.24 (weight ratio)),
and the material powders of the third layer 103 were mixed so that
the carbon concentration became 0.8 wt. % (chrome molybdenum steel
powder A: chrome molybdenum steel powder B=65:35 (weight ratio)),
and the mixed material powders were uniformly mixed by a V-shape
rotating mixer to prepare the material powders of these layers
[0040] FIG. 6 shows a process for forming the first layer, the
second layer, and the third layer in the present example. Each of
the layers were formed using a plasma spraying method. The first
layer, the second layer, and the third layer formed in this order
by changing the material powders in the same conditions. In this
configuration, since each of the layers was partly formed, while
the member under treatment 101 pre-heated at 400.degree. C. was
being rotated, the member under treatment 101 was scanned by a
thermal spray nozzle 106 to form the individual layers at desired
portions as shown in FIG. 6.
EXAMPLE 3
[0041] In the configuration of example 2, the material powders of
the third layer were prepared so that their carbon concentration
became 1.0 wt. % (chrome molybdenum steel powder A: chrome
molybdenum steel powder B=54:46 (weight ratio)) by the plasma
spraying method. The other forming conditions were same as those of
Example 2.
COMPARATIVE EXAMPLE 2
[0042] In the configuration of Example 2, the material powders of
the first layer were prepared so that the carbon concentration
became 0.8 wt. % (chrome molybdenum steel powder A: chrome
molybdenum steel powder B=65:35 (weight ratio)) by the plasma
spraying method, and the second layer and the third layer were not
formed. The other forming conditions of Comparative Example 2 were
the same as those of Example 2.
COMPARATIVE EXAMPLE 3
[0043] In the configuration of Example 2, the material powders of
the third layer were prepared so that the carbon concentration
became 1.1 wt. % (chrome molybdenum steel powder A: chrome
molybdenum steel powder B=49:51 (weight ratio)) by the plasma
spraying method. The other forming conditions of Comparative
Example 3 were the same as those of Example 2.
[0044] The steel parts 100 obtained in Examples 2 and 3 and
Comparative Examples 2 and 3 were smoothened by a mechanical
polishing method or a buffing method so that the surface roughness
(Ra) became 1.0 .mu.m or less. Thereafter, a Falex test was
conducted in lubrication oil for a film-forming portion of the
third layer 103 based on ASTM-D-3233. Table 2 shows the thicknesses
of the individual layers measured by cutting the steel parts 100
after the Falex test was confucted, average carbon concentrations
measured by an electron beam micro-analyzer (SHIMAZU CORPORATION),
presence or absence of inter-layer peeling observed by an optical
microscope, surface roughness (Ra) of the outermost layers, and
cross-sectional Vickers hardness measured by a micro Vickers
hardness meter (SHIMAZU CORPORATION).
[0045] When the Falex test was conducted with an approximately 1-mm
thick test piece having a Vickers hardness (Hv) of 930 or higher on
the surface of steel parts 100 in Examples 2 and 3, surface
treatment layers having excellent adherence without inter-layer
peeling were obtained. It was confirmed that in each of the surface
treatment layers of each sample, mesh-shaped cementite was not
deposited on a grain boundary and the layers did not excessively
carburize.
[0046] In contrast, in Comparative Example 2, there was a problem
in adherence due to small peeling between the member under
treatment 101 and the first layer 102. Further, it was confirmed
that in the conditions of Comparative Example 3, the surface
roughness after the Falex test was conducted was larger than that
of the other steel parts, and the steel part 100 was damaged by
abrasion. As a result of an observation of the composition, it was
confirmed that mesh-shaped cementite that was characteristic of
hypereutectoid steel of a steel material was deposited on a grain
boundary, and an carburized portion was damaged.
[0047] From each of the foregoing evaluations, it was confirmed
that the steel parts having configurations disclosed in the present
invention have a surface treatment layer having excellent surface
hardness and excellent adherence to a member under treatment.
Although a shaft as a machine part has been described in this
section, it is clear that the embodiments of the present invention
can be applied to various machine parts such as drive parts, gears,
and bearings.
TABLE-US-00002 TABLE 2 EXAMPLE EXAMPLE COMPARATIVE COMPARATIVE 2 3
EXAMPLE 2 EXAMPLE 3 FIRST THICKNESS (mm) 0.10 0.10 1.03 0.08 LAYER
AVERAGE CARBON 0.32 0.33 0.78 0.32 CONCENTRATION (wt. %) VICKERS
HARDNESS 610 630 900 610 (Hv) SECOND THICKNESS (mm) 0.11 0.09 0.13
LAYER AVERAGE CARBON 0.55 0.57 0.53 CONCENTRATION (wt. %) VICKERS
HARDNESS 800 820 770 (Hv) THIRD THICKNESS (mm) 0.99 1.05 1.03 LAYER
AVERAGE CARBON 0.77 0.99 1.05 CONCENTRATION (wt. %) VICKERS
HARDNESS 940 930 960 (Hv) SURFACE ROUGHNESS (Ra, .mu.m) 1.1 0.9 2.1
5.4 ADHERENCE BETWEEN BASE NO NO CRACKING NO MATERIAL AND LAYER
PEELING PEELING PEELING
REFERENCE SIGNS LIST
[0048] 100 steel part [0049] 101 member under treatment [0050] 102
first layer [0051] 103 second layer [0052] 104 third layer [0053]
105 spray nozzle [0054] 106 spray nozzle
* * * * *